Evidence for a generic interceptive strategy

Abstract

In the present work, we first clarify a more precise definition of instantaneous optical angles in control tasks such as interception. We then test how well two interceptive strategies that have been proposed for catching fly balls account for human Frisbee-catching behavior. The first strategy is to maintain the ball's image along a linear optical trajectory (LOT). The second is to keep vertical optical ball velocity decreasing while maintaining constant lateral optical velocity. We found that an LOT accounted for an average of over 96% of the variance in optical Frisbee movement, while maintenance of vertical and lateral optical velocities was random. This work confirms a common interception strategy used across interceptive tasks, extending to complex target trajectories.

Chasin’ choppers: using unpredictable trajectories to test theories of object interception

“…Results of trials in those studies where the object changed direction midflight were inconsistent with the LOT hypothesis; the observed optical trajectories of Frisbees, which make unpredictable midflight path changes, were not singular straight lines (Shaffer et al, 2004;Shaffer et al, 2008). This led to the development of the segmented version of LOT (SLOT), which assumes that pursuers maintain a linear optical trajectory of a particular slope until there is an abrupt change in the target's direction, at which point a new linear trajectory (segment) is maintained at a different slope.…”

“…This led to the development of the segmented version of LOT (SLOT), which assumes that pursuers maintain a linear optical trajectory of a particular slope until there is an abrupt change in the target's direction, at which point a new linear trajectory (segment) is maintained at a different slope. Both SLOT and OAC/GOAC were able to account for the optical trajectories observed for dogs chasing Frisbees (Shaffer et al, 2004), but only SLOT could account for the optical trajectories observed for humans chasing Frisbees (Shaffer et al, 2008).…”

“…Pursuer is shown moving laterally and forward in equal temporal intervals (t 1 -t 3 ) to intercept the target (helicopter). The vertical optical angle between the target and the horizon is α; the lateral angle between the target and pursuer is β McBeath, 2002;Shaffer et al, 2008); LOT, and OAC/GOAC have been shown to be consistent with the results of research on fielding ground balls in baseball (Sugar, McBeath, & Wang, 2006); SLOT and COV have been shown to be consistent with the results of research on dogs navigating to catch Frisbees (Marken, 2005;Shaffer et al, 2004); and LOT, OAC, and GOAC have been shown to be consistent with the results of research on robotic navigation for interception (Sugar & McBeath, 2001). …”

“…The first studies of object interception that introduced such midflight disturbances were done by Shaffer et al (2004) and then again by Shaffer et al (2008). Results of trials in those studies where the object changed direction midflight were inconsistent with the LOT hypothesis; the observed optical trajectories of Frisbees, which make unpredictable midflight path changes, were not singular straight lines (Shaffer et al, 2004;Shaffer et al, 2008).…”

“…Navigation Theories of object interception have proposed different control strategies for intercepting objects such as baseballs, cricket balls, Frisbees, and virtual soccer balls (Chapman, 1968;Dienes & McLeod, 1993;McBeath, Shaffer, & Kaiser, 1995McLeod & Dienes, 1996;McLeod, Reed, & Dienes, 2001McLeod, Reed, Gilson, & Glennerster, 2008;Michaels & Oudejans, 1992;Shaffer, McBeath, Krauchunas, & Sugar, 2008;Sugar & McBeath, 2001). Several strategies have been proposed as explanations of the interceptive behavior involving these different types of target objects: linear optical trajectory (LOT; McBeath et al, 1995), optical acceleration cancellation (OAC; Chapman, 1968), generalized OAC (GOAC; McLeod et al, 2006), segmented LOT (SLOT; Shaffer, Krauchunas, Eddy, & McBeath, 2004;Shaffer et al, 2008), and control of optical velocity (COV; Marken, 2001). These object interception strategies differ mainly in terms of the type of optical information that is assumed to be the basis of object interception.…”